Conspectus Transition metal catalyzed asymmetric hydrofunctionalization of readily available unsaturated hydrocarbons presents one of the most straightforward and atom-economic protocols to access ...valuable optically active products. For decades, noble transition metal catalysts have laid the cornerstone in this field, on account of their superior reactivity and selectivity. In recent years, from an economical and sustainable standpoint, first-row, earth-abundant transition metals have received considerable attention, due to their high natural reserves, affordable costs, and low toxicity. Meanwhile, the earth-abundant metal catalyzed hydrofunctionalization reactions have also gained much interest and been investigated gradually. However, since chiral ligand libraries for earth-abundant transition-metal catalysis are limited to date, the development of highly enantioselective versions remains a significant challenge. This Account summarizes our recent efforts in developing suitable chiral ligands for iron and cobalt catalysts and their applications in the highly enantioselective hydrofunctionalization reactions (hydroboration and hydrosilylation) of alkenes and alkynes. In ligand design, we envisioned that chiral unsymmetric NNN-tridentate (UNT) ligand scaffolds could promote these enantioselective transformations with earth-abundant metals. Therefore, several types of chiral UNT ligands were designed and prepared in our laboratory, utilizing readily available natural amino acids as chiral sources. In the very beginning, chiral oxazoline iminopyridine (OIP) ligands were proposed and investigated through the rational combination of nitrogen-containing ligand scaffolds. After a systematic survey of the ligand effects, the imine moiety in the rigid OIP ligands was replaced by a conformationally more flexible amine unit, leading to the construction of reactive oxazoline aminoisopropylpyridine (OAP) ligands. Subsequently, imidazoline iminopyridine (IIP) and thiazoline iminopyridine (TIP) ligands were prepared by altering the oxygen atom of oxazoline with nitrogen and sulfur linkers, respectively. To further expand the chiral ligand library, other tridentate ligands containing a twisted pincer, anionic, and nonrigid backbone were also designed and synthesized, including iminophenyl oxazolinyl phenylamine (IPOPA) and imidazoline phenyl picolinamide (ImPPA). The efficacy of these chiral UNT ligands for asymmetric induction in iron and cobalt catalysis has been demonstrated through asymmetric hydrofunctionalization of alkenes and asymmetric sequential hydrofunctionalization of alkynes, which exhibit excellent reactivity as well as high chemo-, regio-, and stereoselectivity with broad functional group tolerance. Notably, highly regio- and enantioselective hydrofunctionalization of challenging substrates, such as 1,1-disubstituted aryl alkenes and terminal aliphatic alkenes, was also achieved. Furthermore, the development of asymmetric sequential isomerization/hydroboration of internal alkenes and sequential hydrofunctionalization of alkynes further demonstrates the synthetic power of these catalytic systems. The chiral enantioenriched products obtained by these methodologies could be potentially utilized in organic synthesis, medicinal chemistry, and materials science. We believe that our continuous efforts in this field would be beneficial to the development of asymmetric earth-abundant metal catalysis.
Recent years have witnessed the growing interest in the remote functionalization of alkenes for it offers a strategy to activate the challenging C-H bonds distant from the initiation point via alkene ...isomerization/functionalization. However, the catalytic enantioselective isomerization/functionalization with one single transition metal catalyst remains rare. Here we report a highly regio- and enantioselective cobalt-catalyzed remote C-H bond borylation of internal alkenes via sequential alkene isomerization/hydroboration. A chiral ligand featured twisted pincer, anionic, and non-rigid characters is designed and used for this transformation. This methodology, which is operationally simple using low catalyst loading without additional activator, shows excellent enantioselectivity and can be used to convert various internal alkenes with regio- and stereoisomers to valuable chiral secondary organoboronates with good functional group tolerance.
Highly regio- and enantioselective intermolecular hydroamination of alkenes is a challenging process potentially leading to valuable chiral amines. Hydroamination of alkenes via metal-catalyzed ...hydrogen atom transfer (HAT) with good regioselectivity and functional group tolerance has been reported, however, high enantioselectivity has not been achieved due to the lack of suitable ligands. Here we report a ligand-promoted cobalt-catalyzed Markovnikov-type selective radical hydroamination of alkenes with diazo compounds. This operationally simple protocol uses unsymmetric NNN-tridentate (UNT) ligand, readily available alkenes and hydrosilanes to construct hydrazones with good functional group tolerance. The hydrazones can undergo nitrogen-nitrogen bond cleavage smoothly to deliver valuable amine derivatives. Additionally, asymmetric intermolecular hydroamination of unactivated aliphatic terminal alkenes using chiral N-imidazolinylphenyl 8-aminoquinoline (IPAQ) ligands has also been achieved to afford chiral amine derivatives with good enantioselectivities.
In a stochastic Stackelberg asymmetric security game, the strong Stackelberg equilibrium (SSE) strategy is a popular option for the defender to get the highest utility against an attacker with the ...best response (BR) strategy. However, the attacker may be a boundedly rational player, who adopts a combination of the BR strategy and a fixed stubborn one. In such a condition, the SSE strategy may not maintain the defensive performance due to the stubbornness. In this paper, we focus on how the defender can adopt the unilateral-control zero-determinate (ZD) strategy to confront the boundedly rational attacker. At first, we verify the existence of ZD strategies for the defender. We then investigate the performance of the defender's ZD strategy against a boundedly rational attacker, with a comparison of the SSE strategy. Specifically, when the attacker's strategy is close to the BR strategy, the ZD strategy admits a bounded loss for the defender compared with the SSE strategy. Conversely, when the attacker's strategy is close to the stubborn strategy, the ZD strategy can bring higher defensive performance for the defender than the SSE strategy does.
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•Optimal rolling processes promoted the uniform microstructure, leading to low iron loss.•Optimal rolling processes furthered magnetic induction with λ-fiber and α* texture.•Great ...mechanical and magnetic properties were obtained by coherent Cu-rich clusters.
A bottleneck in the development of high-strength non-oriented silicon steels for drive motors of new energy vehicles is the balance of strength and magnetic properties. This paper successfully tackled this problem through the optimization of thickness reduction for hot and cold rolling and the formation of coherent precipitates using a Cu-alloyed non-oriented silicon steel. More specifically, a thickness reduction of 96% in the course of hot rolling promoted the homogenization of microstructure during the following normalization treatment. Subsequently, a deformation degree of 80% during cold rolling ensured the inheritance of the uniform microstructure and inhibited the abnormal growth of recrystallized grains during annealing, thereby suppressing the iron loss to a value as low as 15.6 W/kg. At the meantime, this combined process promoted the inheritance of λ-fibers and the formation of {114}〈481〉 texture in the annealed sheet, improving the magnetic induction intensity B50 to 1.606 T. In addition, under the joint effect of a variety of strengthening mechanisms, the yield strength of this annealed sheet reached 668 MPa. A pronounced increase in strength, about 207 MPa, was derived from precipitation hardening by the great difference in the modulus between coherent Cu-rich clusters and the α-Fe matrix.
Zero-determinant (ZD) strategies have attracted wide attention in Iterated Prisoner's Dilemma (IPD) games, since the player equipped with ZD strategies can unilaterally enforce the two players' ...expected utilities subjected to a linear relation. On the other hand, uncertainties, which may be caused by misperception, occur in IPD inevitably in practical circumstances. To better understand the situation, we consider the influence of misperception on ZD strategies in IPD, where the two players, player X and player Y, have different cognitions, but player X detects the misperception and it is believed to make ZD strategies by player Y. We provide a necessary and sufficient condition for the ZD strategies in IPD with misperception, where there is also a linear relationship between players' utilities in player X's cognition. Then we explore bounds of players' expected utility deviation from a linear relationship in player X's cognition with also improving its own utility.
In this paper, the effect of temper rolling and final annealing on microstructure, texture and magnetic properties of a 0.6 wt% Si non-oriented electrical steel, with 5.7% temper rolling reduction, ...were investigated via EBSD and XRD three-dimensional orientation distribution function (ODF) analysis. The results indicate that final annealing plays an essential role in improving the magnetic properties of non-oriented electrical steels. The core loss decreases with the increasing annealing time, reaches the lowest value at 10 min, and then tends to be stable. The magnetic induction quickly increased with prolonged annealing time, reached the highest value, then decreased slightly to a lower value after 15 min. The peak permeability increased rapidly with the increasing annealing time, reached the highest value after 3 min, and became stable after 10 min. The grains abnormally develop from the sample surface to the inner layer derived from gradient strain. Before and after temper rolling, the texture of the material is mainly dominated by {111} . As annealing time increases, the intensity of {111} decreases, emerging the weak Goss ({110} ) and other orientations. Finally, there are without preferred orientations when time exceeds 10 min.
The optimization of magnetic and mechanical properties by microstructure modification is tremendously challenging for high-grade non-oriented silicon steel. In the current study, the microstructure ...of cold-rolled high-grade non-oriented silicon steel was modified by recrystallization annealing to achieve high strength and good magnetic properties. The results indicate that recrystallization annealing significantly improved the magnetic properties, while negatively impacting its mechanical properties. At the early stage of annealing (<2 min), recrystallization nucleation occurred in the deformation matrix, leading to a significant decrease in dislocation density. This decrease in dislocation density resulted in a notable reduction in coercivity and hence enhancement in magnetic properties. However, the mechanical properties deteriorated due to the elimination of dislocations. With further increasing the annealing time (>2 min), the recrystallization grains grew within the fully recrystallized matrix. There was a slight decrease in both dislocation density and grain boundary density, leading to a slight decrease in iron loss and yield strength. The magnetic induction intensity of the fully recrystallized annealed sheets was primarily influenced by the recrystallization texture. Thus, the critical annealing time was 2 min to meet the demands of both magnetic and mechanical properties for the studied high-grade non-oriented silicon steel.
In this work, the non‐metallic inclusions contained in a trial X70 pipeline steels are characterized by optical microscopy, scanning electron microscopy, energy‐dispersive X‐ray spectrum, and ...transmission electron microscopy. Statistical analysis is conducted to summarize the size and shape of the inclusions. The hydrogen trapping and the resulting hydrogen‐induced cracking (HIC) susceptibility of the steels are tested. Density functional theory is used to calculate the binding energy of hydrogen at MnS inclusions, and the impact of MnS inclusions on hydrogen trapping and the HIC susceptibility is evaluated. It is found that the majority of submicron scale inclusions are MnS, which serve as irreversible hydrogen traps. The content of the trapped hydrogen can be effectively decreased by controlling the size of MnS inclusions below submicron scale and distributing the inclusions uniformly in the steel. As a result, the susceptibility of the steel to HIC is reduced.
Density functional theory is used to calculate the binding energy of hydrogen at MnS‐matrix interface. The effect of submicron scale MnS inclusions on hydrogen trapping and the susceptibility of HIC are evaluated. It is found that the submicron scale MnS inclusions can serve as irreversible hydrogen trappers, which effectively decrease the amount of mobile hydrogen in steel and promote the resistance against HIC.
The orientation relationships between the coating and the substrate after galvanizing (GI) and galvannealing (GA) have been studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). ...The δ phases in the coatings predominantly have
,
and
plane textures and showing the semi-coherent relationship with the {111} plane of the substrate. It has been found that these types of texture components are essential for the bond between the coating and the substrate. The percentage of
,
and
texture components increases initially with the increase of the holding time during the GA process before decreasing.
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